How did the Roman Empire survive the huge problems it faced during the crisis of the Third Century? In my extended review of the Decline and Fall of the Roman Empire I have just reached the reign of Diocletian. But before moving forward I'd like to have a look at what it was about the Roman world at this time that enabled it to emerge almost as big and powerful from the crisis as when it went into it. My answers are largely drawn from a very interesting audio book by Thomas Madden from the Modern Scholar series called The Tiber and the Potomac.

As far as I can tell the Tiber and the Potomac is only available in audio format which is a pity - it would make a very good book. I don't know a great deal about Thomas Madden at the moment but I will be looking into his other work to see if he has any other stuff in a fairly popular style.

So what has he got to say? He divides empires into three categories. Empires of conquest are the simplest to understand and historically speaking are the standard model for an empire. The concept is self explanatory. You attack your neighbour and force him to obey you, or you take his property or both if you feel like it. Then carry on the process until you have a large enough area to meet your desired level of domination and supremacy.

Empires of conquest last for as long as they are able to maintain a reasonable level of intimidation, but can collapse quite quickly, probably accompanied by a sigh of relief from the conquered.

Empires of commerce are a bit more subtle. The purpose of an empire of commerce is to facilitate the trade of the empire builder. The power of the arrangement comes from the economic power of the trading country over its trading partners. An early example would be Rome's neighbours the Carthaginians. Carthaginians did of course use force when necessary to protect their commercial interests. But even this was pretty much a business arrangement with the bulk of the troops being mercenaries hired to do a job, presumably after some accountant had checked out whether the project was cost effective.

The most familiar example of a commercial empire is the British Empire. It is worth remembering that the informal empire was quite a big bigger than the official one. A country like Argentina for instance which was developed almost exclusively by British capital was just as much in the British sphere as some of the actual colonies. Britain fought relatively few wars of conquest. There was much more fighting against trading rivals than the populations who were already there. It speaks volumes that the original conquest of India was carried out not by the British government but by an independent entity callled the East India company.

So what kind of empire was the Roman Empire? Madden argues that it was a third kind of empire, an empire of consent. What's that then?

Basically the Romans started out as farmers living on the margins of civilisation. On one side were the barbarian Gauls who could at any moment attack and wipe out the Romans. On the other side were the large organised urban centred empires of Carthage, Greece and Persia. These could attack at any moment and wipe out the Romans. The Romans weren't motivated by trade or ambition. Their problem was security.

The problem was shown in stark relief in 390BC when the Gauls attacked and sacked Rome. The Romans had alliances with some of the neighbouring cities that should have ensured common front against the enemy, but faced with a large force of ferocious barbarians the allies decided that they would keep a low profile and leave the Romans to face them alone. The Gauls looted the city and wouldn't go away until the Romans paid them 1000 pounds of gold.

This disaster led to the Romans overhauling their diplomatic system. The system of alliances was strengthened and was backed up with more forceful military measures. There was also a move to extend the system further out to ensure that action could be taken at an earlier stage before the barbarians were at the gate (a rare non-methaphorical use of that phrase). Madden calls it widening the horizon of security.

This is the way it worked. Imagine big city A is pushing around small city B. The Romans would turn up and offer to support B in return for a binding alliance and some mutually beneficial concessions. This would highlight to other smaller cities the advantages of closer ties with Rome. Faced with the impossibility of acting aggressively and now at risk from attack by Rome itself, A would generally sign up too. As the system grew so did the advantages of joining up. It would obviously work better the more trustworthy and responsible that Rome behaved - which was where its legalistic and republican traditions helped. If you came to an agreement with the Romans you were entering into a legally binding contract with the Senate, rather than placing your trust in a prince who could possibly change his mind and would definitely at some point die.

So we can now interpret Rome's early rise in the peninsula of Italy as a steady extension of a system of alliances rather than the Romans simply conquering everyone else. There was fighting to be sure, but the fighting was not to defeat and subjugate all non-Romans. The conflicts were with other potential leading powers. And the success of Rome was at least as much due to the good behaviour and trustworthiness of the Romans as to the strong performance of their army.

This was made very clear by the time the Roman system had reached the south of Italy and the Romans had come into contact with the Greek cities of the region. The leading city in the district was Tarantum. The citizens of Tarantum would probably have known the saying of Thucydides that strong cities do as they please, while weak cities endure what they must. In any event, they were doing as they pleased. Some of their victims allied themselves to Rome in the hope of getting even. The Romans sent diplomats to press their new allies' case. The Greeks of Tarantum were contemptuous, mocking the Romans' togas and their poor ability to speak Greek. They were obviously not bothered by the prospect of the full scale war with Rome that this caused.

Their swagger was backed up by their secret weapon. They had contracted the former king of Macedonia, Pyrrhus as a hired gun. He only had a small kingdom at that time but he had a very effective army, and as a cousin of Alexander the Great had prestige as well. At this time a Greek army was the height of military sophistication and Pyrrhus was able to reliably defeat the Romans in pitched battle. However he was only able to do this with large losses. This is the origin of the term Pyrrhic victory for a victory that is so costly that it negates the benefits of the victory itself.

In fact it is easy to exaggerate his losses. His problem was that his army was at that point his only asset so it is not surprising that he was unwilling to risk casualties that would weaken his only strong card in his struggle to regain his throne. This made him very sensitive to losses. But whatever, he decided that he would take the fight to Rome itself. The strategy was simple. He would march on Rome liberating cities as he went along and so building support and increasing his forces as he went. It sounded like a realistic plan, particularly when your army can carry all before it on a battlefield. What could go wrong?

Well what went wrong was that the people he was liberating showed very little inclination to be liberated. Even with the persuasive power of the army of Pyrrhus, life with the Romans seemed preferable to life on their own. Although never actually defeated, Pyrrhus ended up leaving without doing any damage to the position of Rome. Rome had triumphed not through superior military power but because it commanded the consent of the populations under its control.

The appeal of Roman protection was later strong enough to bag them whole kingdoms without a fight. Attalus of Pergamon left his city to Rome in his will. And this wasn't an isolated example. There were several episodes in Roman history when people actively tried to get into the empire and its protection.

I'll get onto what all this means for the Third Century crisis, but I can't skip over the main point of the Professor's book which is to draw parallels between the Roman empire and the American empire. What American empire you might ask? America does control directly a few military bases around the world, but it is hardly an empire on a par with say the British Empire, or even the Belgian one. But the point is that at least up until the reign of Augustus, and possibly for longer afterwards an educated Roman might well deny just as vehemently as a modern American that they possessed an empire. They didn't rule over people, they just had lots of friends.

And they would be right on paper. Relatively little of what we now call the Roman Empire was directly ruled as a province initially. But of course the Roman Army was there and all the important decisions were taken in Rome. Does this sound at all familiar? In Western Europe there are no American provinces. But there are over 100,000 American troops. And at the very least, Europeans have to take some notice of what goes on in the US.

The Tiber and the Potomac is interesting throughout, but the most fascinating bit of it for me was the account of the love-hate relationship between the Greeks and the Romans. How did Rome end up in Greece? It was an extension of the same style of diplomacy that had given Roman effective control of Italy. The Greek city states were threatened by Philip of Macedonia. The Romans stepped in to protect the Greeks and conquered Philip. The Greeks were now free of the threat of Philip, but were now occupied by the Romans. What would the Romans do? Remarkably they withdrew their troops and left the Greeks to govern themselves.

At the meeting where this decision was related to the representitives of the Greeks, the cry of acclamation from the crowd was so loud it is reported to have knocked birds out of the sky.

There is no doubt that the Romans respected and felt in debt to Greek culture. But this was to become mingled with a certain amount of contempt. Sure, they were clever and all that. Astronomy, mathematics, philosophy were all very impressive. But at the end of the day it was the down to Earth common sense Romans who were actually running the show.

Does that sound a bit like some Americans' attitude to Europeans? On the one hand, Paris and London are always full of American tourists on the look out for culture. On the other it wasn't that long ago that one of the leading nations of Europe was being derided in Washington as a bunch of cheese eating surrender monkeys. When Barak Obama confessed to being embarassed that he couldn't speak any foreign languages and suggested that it would be a good idea if more Americans learned them, he was attacked by critics.

You would have thought that having a president who not only reads books, but has managed to actually write one would be a good thing. But his enemies are not looking for a figurehead to match him intellectually. At time of writing this the best known American politician after Obama himself is Sarah Palin, who seems to play on her lack of sophistication and homespun values. Mystifying as these attitudes are to a modern European, the plain talking go getting Romans would probably have sympathised with them.

The ambiguity of the relationship between the Greeks and the Romans worked on both sides. The Greeks gratituded to the Romans for saving them from Philip did not last long. Another threat arose. Antiochus of Syria attempted to invade Greece. He was rapidly pushed back by the Romans who proceeded to push him out of Asia Minor and organise the Greek cities there along the same lines that they had already done on the Greek mainland. But by now many Greeks sided with the enemies of Rome and in Corinth some Roman soldiers were killed in anti-Roman demonstrations. Corinth is of course a long way from Syria. The Greeks who lived closer to Antiochus were a bit more pro-Roman.

But the Romans were fed up with the attitudes of the Corinthians and sacked their city, this in 146 BC. Corinth itself was smashed, but other Greek cities were allowed a nominal independence. So a lot of Greeks found themselves as allies of Rome. On paper they had the option of withdrawing from the alliance and making their own way in the world. But the plain fact was that the Greeks were in no position to do anything about the Romans. The Romans generally didn't give the Greeks a hard time and indeed went to some trouble to soothe their battered egos. In reality the Greeks were better off inside the Roman sphere than they would have been outside it - but they didn't get the option of choosing.

It all sounds very much like European anti-Americanism. It wasn't hard to find people willing to criticize the US even at the height of the Cold War in western Europe. De Gaulle was even able to pull France out of the military wing of NATO without any trouble from French voters. France is a fair way from Russia in the same way that Corinth was pretty far from Syria. But the reality was that not many Europeans would have preferred to fall under the influence of the Soviet Union instead, which was the actual choice.

So the parallel between the way the Roman Empire came to be and the way an American Empire seems to be forming is pretty close. I was reminded of this analysis when following the coverage of the latest round of defence cuts on the Royal Navy. The navy that Britain will have when the axe has been wielded is hardly worthy of the name of a navy. To all intents and purposes a country that once ruled the waves will barely be able to patrol its own shores. But it makes perfect sense. What after all, could be done with a navy the size it was at its peak in 1945 with 950 ships? It would still not be enough to challenge the US navy even locally. The US will not allow anyone to attack Britain, nor would they allow Britain to attack anyone else. Why pay to fund a fleet you can't use?

So that is the Pax Americana. The overwhelming military superiority of the US makes the world a safe place, particularly if you are an ally of the US. In fact, if you are an ally of the US your best option is not just to not build your own forces up. You are better off with the minimum you can get away with. I think the Irish are the ones who take this furthest. The Irish army is less than 10,000 strong and with no tanks and little artillery would probably struggle to beat off an attack by Narnia. But an attack by anyone else seems hardly more likely.

The Pax Americana is very similar to the Pax Romana of 2000 years before. The provincials inside the empire soon realised that there was no longer any need for them to bear arms. The legions would keep the barbarians out. The nominally independent states tended to become colonies in time, but this was just an acknowledgment of reality. The decisions were made in Rome, so if something needed doing that was where they went to get it done. Roman citizenship was gradually extended, first to Latin allies then other Italians. As the empire grew wider co-operative provincials were rewarded with citizenship as well. More and more people came to have a stake in the empire.

The end of the republic must have weakened the trust in the empire to some extent. Power welded in the hands of a single man who at least potentially is above the law is not as reliable as a legally based republic. But even so, most of the building blocks of the empire of trust - particularly the army - were still in place.

By the reign of Caracalla, citizenship was already very widespread. He took the logical next step of giving it to everybody. So by the Third Century it was quite feasible for large numbers of people to think that it was their empire. If they worked hard and acquired wealth, or joined the army and did well they could aspire to become Senators or even Emperor. And there was no alternative to the empire either. Religion was not at that time a huge motivator. Political ideologies and nationalism were not yet known either. So there was no reason to oppose the empire, and in a world still full of barbarians every reason to support the regime whose legions could defend you.

So despite the huge blows that the empire suffered in the crisis of the Third Century, there were pressures that were pushing it back together again. It offered peace and security in a dangerous world. And with a good emperor it also offered justice, free bread and top notch low cost entertainment. What's not to like? The Roman Empire proved a lot more resilient than any observer would have predicted. At the end of the day and for all its faults, people liked it. I wonder if the American Empire will prove to be as surprisingly tenacious?

If you want to follow my extended review of Decline and Fall of the Roman Empire from the beginning (and who wouldn't?) it starts with Augustus founding the empire.